Solar concentrators are widely used to enhance the performance of solar cells.
The aim of solar concentrators is to collect incident radiation over a large surface and concentrate the energy to its edges where it is collected by solar cells or photovoltaic (PV) cells. Thus, the incident sunlight is focussed to the surface of the solar cell thereby increasing the power density of radiation which is subsequently converted into electric energy.
A well-known form of solar concentrators is a so called luminescent solar concentrator (LSC). A luminescent solar concentrator generally comprises a collector being designed as a flat and optically transparent or semi transparent sheet. This sheet often is formed of a material such as glass, polymer, or the like. The collector comprises or is coated with a luminescent substrate which absorbs the incident sunlight and emits light at longer wavelengths. Generally, the light of longer wavelengths is emitted in all directions. A substantial fraction of the emitted light however is captured in the sheet and is transported, via total internal reflection, to at least one edge of that flat sheet and thus to the surface of a solar cell, thereby concentrating the light from a large surface (the surface of the sheet) to a smaller surface (the surface of the edge). This effect is widely known as the “edge glow effect”. The ratio of the light intensity at the surface area of the output (i.e. the edge) and to the light intensity at the surface area of the input (i.e. the collection area) is the so called concentration ratio.
In order to improve the concentration ratio, it is known to provide a filter or mirror on the surface of the solar concentrator. This filter has the objective to prevent the emitted radiation from leaving the luminescent solar energy concentrator and thus to prevent the emitted radiation from getting lost. However, this filter not only reflects the light being emitted from the inside of the collector but may also (at least partially) reflect incident sunlight. This leads to less sunlight entering the solar concentrator and thus decreasing the amount of light being guided to the solar cell.
The major drawback of these conventional luminescent solar concentrators is the insufficient concentration ratio leading to a great loss of radiation which is not used by the solar cell.